What to do and what not to do in serological

What to do and what not to do in serological
diagnosis of pertussis: Recommendations from EU
reference laboratories
Nicole Guiso1, Guy Berbers2, Norman K. Fry3, Qiushiu He4, Marion Riffelmann5, Carl Heinz Wirsing
von König§5 for the EU Pertstrain group*
(*Members of the EU Pertstrain group are listed in the appendix)
1: Institut Pasteur, Paris, France
2: National Institute for Public Health and the Environment, Bilthoven, the Netherlands
3: Health Protection Agency Centre for Infections, London, UK
4: National Institute for Health and Welfare, Turku, Finland
5: HELIOS Klinikum Krefeld, Germany
§ Corresponding author:
Prof. Dr. Carl Heinz Wirsing von König
Institut für Hygiene und Labormedizin
HELIOS Klinikum Krefeld
Lutherplatz 40
D-47805 Krefeld, Germany
Phone +49 2 151 32 24 67
Fax: +49 2 151 32 20 79
e-mail: [email protected]
1
Abstract
Bordetella pertussis specific antibodies can be detected by ELISA or multiplexed immunoassays.
Assays use purified or mixed antigens, and only pertussis toxin (PT) is specific for Bordetella
pertussis. The interpretation of results can be based on dual sample or single sample serology using
one or two cut-offs. The EU Pertstrain group recommends that (i) ELISAs and multiplexed
immunoassays should use purified non-detoxified PT as an antigen, that they should have a broad
linear range, and that they should express results quantitatively in International Units per millilitre
(IU/ml). (ii) a single or dual diagnostic cut-off for single serum serology using IgG-anti-PT between
50 IU/ml and 120 IU/ml should be used, and diagnostic serology cannot validly be interpreted for one
year after vaccination with acellular pertussis (aP) vaccines (iii) IgA-anti-PT should only be used with
indeterminate IgG-anti-PT levels or when a second sample cannot be obtained.
This group discourages using (i) other antigens in routine diagnostics, as they are not specific. (ii)
micro-agglutination due to its lack of sensitivity. (iii) immunoblots for pertussis serodiagnosis, as
results cannot be quantified and (iv) other methods, such as complement fixation or indirect
immunofluorescence, due to their low sensitivity and/or specificity
Word count: 195
2
Indications for pertussis diagnostics
Diagnosis of pertussis should only be attempted in patients with symptoms compatible with pertussis,
such as prolonged coughing with paroxysms and/or whooping or choking. In infants, older vaccinated
children, adolescents and adults the clinical course may not be typical, and prolonged coughing may
be the only symptom. In these cases, diagnosis of pertussis requires laboratory methods for
confirmation.
Direct and indirect tests are available. Direct tests are real-time PCR and culture whereas indirect tests
measure specific antibodies in oral fluid or sera. Here, we focus on the detection of antibodies against
B. pertussis antigens.
Development of the recommendations
The EU Pertstrain group consists of representatives of the Bordetella reference laboratories in their
respective EU countries. In a face-to-face meeting in the Istituto Superiore di Sanita (ISS) in Rome in
2009, the outline of a manuscript was discussed and agreed upon. After a search of relevant databases,
a first draft was written (NG) and intensively reviewed by members of the group. In a second face-toface meeting in the Rijksinstituut voor Volksgezondheid en Milieu (RIVM) in June 2010, the draft
recommendations were broadly discussed and agreed upon. A second version of the recommendations
was drafted (NG, CHWvK). This version was then reviewed again by all authors.
Serological tests
Blood / Serum
Most serological assays are validated to test serum; some may also be validated to test heparinised
plasma or EDTA-plasma. Capillary blood samples may be used if a sufficient volume can not be
obtained otherwise. Serum or plasma must be separated as soon as possible after blood sampling (24h
at room temperature). If acute and convalescent serum samples taken at least three weeks apart from
one individual are available, they should be tested together in one run. All serum samples may be
frozen (at -20°C) after the primary assay and reanalyzed later together with a possible second sample.
3
ELISA in serum samples: In preparation for the acellular vaccine studies in the 1990s, the ELISA
methodology, the type of antigens as well as the reference sera have been standardized, and they have
been used in all acellular vaccine trials, in sero-epidemiological studies in many countries, and for
diagnostic purposes in various laboratories [1-5].
Antigens: ELISA is normally done with highly purified antigens. The antigens most
frequently used are PT, and FHA, and to a lesser extent Pertactin (PRN) and Fimbriae (FIM).
Sometimes Adenylate Cyclase-hemolysin Toxin (ACT) is also used. These antigens are used in their
active, i.e. non-detoxified form. The storage conditions of the antigens as well as the duration of
storage can vary significantly according to the manufacturers who provide the purified antigens. AntiPT antibodies are specific for B. pertussis, whereas anti-FHA, anti-PRN, anti-FIM and anti-ACT are
less specific due to cross-reactivity with other microbial antigens (eg. other Bordetella species,
Haemophilus species, Mycoplasma pneumoniae, Escherichia coli). For this reason, in routine
diagnosis, only measurement of anti-PT antibodies is recommended. However, measurement of other
antibodies may be used for transmission, immunogenicity or vaccine non-inferiority studies. Some
ELISAs, especially commercial kits, use a mixture of antigens or supernatants or sonicates of whole B.
pertussis cells. The use of kits with mixed antigens is not recommended (Riffelmann et al. submitted).
Reference sera: WHO references are available from the NIBSC (Potters Bar, UK) (“WHO
International Standard (06/140)” and “WHO Reference Reagent (06/142)”) for the measurement of
human antibodies to B. pertussis antigens, and thus quantitative results should be reported IU/ml [6].
Plates: For in-house ELISAs differences between plates were observed, and Thermo Scientific
Nunc Maxisorp (Nunc AS, Copenhagen, Denmark) plates and Greiner Microlon High Binding
(Greiner Bio-One, Frickenhausen, Germany) plates seemed to work better than others [7].
Flow cytometry: Bead based multiplex assays that simultaneously measure antibodies to various
antigens have also been applied to B. pertussis antigens. The assays use fluorescent microparticles to
which purified antigens are covalently coupled and are based on a proprietary method patented in
1983 in Germany [8] or on xMAP technology from LuminexTM [9]. These assays seem to produce
results comparable to conventional ELISA systems.
4
Immunoblots, line- and dot-blots: Many commercial kits detect anti-B. pertussis and/or anti-PT,
anti-FHA, anti-PRN and also ACT antibodies in serums using blotting techniques. Kits using whole
cell suspensions as antigens are not specific for the detection/diagnosis of pertussis infections due to a
lot of cross-reactivity with other bacteria (eg. other Bordetella species, Haemophilus species,
Mycoplasma pneumoniae). Antigens used in these kits have to be validated concerning their purity, as
contaminations with other antigens or antigen aggregates can also produce false positive results. A
quantitative interpretation of blot results is not possible; a semi-quantitative reporting may be possible.
Although various CE marked commercial kits are available, a recent comparison showed significant
differences between kits and an insufficient correlation to the values of the 1st International Reference
preparation (Riffelmann et al. submitted).
Consequently, the use of immunoblots for pertussis
serology is not recommended by the EU Pertstrain group.
Micro-Agglutination: Micro-agglutination has been widely used before ELISA systems became
available [10]. As with other bacterial agglutination assays, micro-agglutination with B. pertussis cells
mainly measures IgM-antibodies to outer surface antigens such as FIM, PRN and lipooligosaccharide
(LOS). Results are reported in titres starting at 1:20 or 1:40. No agglutinin titre has been attributed to
the WHO reference preparation so far. Agglutinating antibodies can be used to measure the exposure
of a population to B. pertussis antigens; on an individual level the micro-agglutination method is not
useful for confirming the clinical diagnosis of pertussis.
CHO cell neutralization: This test used the ability of PT to induce characteristic morphological
changes in a culture of chinese hamster ovary (CHO) cells. These changes can be neutralized by the
presence of anti-PT antibodies. The titres of CHO-cell neutralizing antibodies correlate well with the
IgG-anti-PT ELISA values, and thus CHO cell assays are rarely used for diagnostic purposes [7,11].
The interpretation of CHO assays cannot be standardized, and it is difficult to interpret the
morphological changes and to score the results objectively.
Complement fixation: Complement fixation using whole cells of B. pertussis has been rarely used
and suffers from lack of sensitivity and specificity.
Indirect immunfluorescence: Indirect immunofluorescence using whole cells of B. pertussis has the
same disadvantages as complement-fixation
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Oral fluid
Oral fluid can be sampled by standardized means, e.g.. Oracol swab (Malvern Medical Developments)
or Orasure oral specimen collection devices (Orasure Technologies Inc.). The diagnostic sensitivity of
measuring antibodies in oral fluid samples is lower (~80%) as compared to serum samples, but the
samples can easily be obtained and offer an adjunct to diagnostic serology
ELISA in oral fluid: An IgG-capture ELISA capable of detecting anti-PT IgG in oral fluid has been
developed. The assay was evaluated by comparison to a serum ELISA. The results showed that the
oral fluid assay detected seropositive subjects with a sensitivity of 79.7% [95% confidence interval
(CI) 68.3–88.4] and a specificity of 96.6% (95% CI 91.5–99.1) relative to the ELISA [12]. This assay
has since been modified to include a monoclonal capture antibody however no commercial assays for
measuring antibodies in oral fluid are available.
Reporting of serological results using ELISA or flow cytometry
Concentrations of antibodies to B. pertussis antigens should be quantitatively expressed in IU/ml as
reference preparations are available [6]. The reference preparation defines values for antibodies of
isotypes IgG and IgA to PT, FHA, PRN, and to FIM. Assigned values of the reference preparation are
described in table 1. The numerical values of IU/ml are equivalent to the previously used ELISA
units/ml (EU/ml) derived from the human reference preparations lot 3, lot 4, and lot 5 from
CBER/FDA, Bethesda, MD, USA.
Interpretation of serological results
PT and FHA are contained in substantial amounts in all acellular vaccines licensed in Europe (except
in Denmark), and PRN and FIM are also components of licensed acellular pertussis vaccines. Thus,
the immune response against infection or vaccination cannot be distinguished and pertussis
vaccination may interfere with the interpretation of serological results. Due to a continuous circulation
of Bordetellae in the population, IgG-anti-PT and other antibodies to Bordetella antigens are
detectable in the majority of all adolescent and adult populations tested so far [13]. Thus, serological
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diagnosis of pertussis must be performed in immunological non-naïve populations with different
kinetics of antibody production.
Additionally, pertussis serology suffers from various other drawbacks:
-
Commercial ELISAs are of different antigen composition and quality,
-
Reference antigens with good purity are not easily available
-
Population-based cut-offs for single-sample serology may need verification after
changes in the vaccination schedule,
-
Interpretation of anti-PT concentrations in recently vaccinated persons is difficult.
Dual sample serology based on ≥100% increase in antibody concentration or on ≥100% decrease in
antibody concentration is a sensitive and specific way for serological diagnosis [1,4]. However, even
in paired sera no antibody increase may be seen after infection due to the secondary immune response,
and the diagnosis may also be based on a decrease of antibodies, which may be too slow to reach 50%
between the acute and convalescent sample.
In clinical practice, diagnosis is mostly based on single sample serology using a single or a more
continuous cut-off. For single-sample serology various cutoff-values for IgG-anti-PT have been
proposed (Table 2): In Massachusetts, 100 EU/ml was used, and later, in order to increase specificity
>~200 EU/ml IgG-anti-PT (>20µg/ml) was employed. In the Netherlands, a cutoff >~125 EU/ml IgGanti-PT with higher specifity or 62 EU/ml with slightly lower specificity has been used [14,15]. In
Germany, a cut-off of ~50 EU/ml IgG-anti-PT was suggested, together with ~50 EU/ml IgA-antiFHA. A seroepidemiological survey was recently performed in various countries in Western Europe
using a cut-off of 125 EU/ml for recent infection, and it can be used as a population based reference
[13]. Another recently completed sero-surveillance in US sera found that three populations could be
separated according to their levels of IgG-anti-PT: one cut-off was estimated at 94 EU/ml, and a lower
cut-off was estimated at 48 EU/ml [16]. Using the lower 50 EU/ml cut-off may be especially useful in
outbreak situations, and overall this cut-off of 50 EU/ml seems to be more adapt for diagnosis rather
than a higher cut-off with lower sensitivity [17].
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Overall, it is astonishing that, irrespective of various vaccination strategies, cut-offs for single sample
serology are comparable throughout the countries where they were evaluated.
A comparison of ROC curve analyses with data from Denmark, the Netherlands, and the UK showed
for all three countries that the single cut-off with optimal sensitivity and specificity may be in the
range between 60 IU/ml and 75 IU/ml.
It may be sensible to use dual a cut-off between 62-125IU/ml according to countries as a proof of a
recent infection with B. pertussis provided that the patient was not vaccinated during the last twelve
months (Table 2). If diagnosis cannot be established with certainty from a single serum, but is deemed
to be necessary according to the clinical symptoms, antibodies should be measured in a second
(convalescent) serum sample at two to four weeks interval. In case of non-availability of a second
serum sample, measurement of IgA anti-PT antibodies can be an alternative, but no broadly accepted
cut-off is available for this antibody subclass. Considering its relatively high specificity and low
sensitivity, a cut-off near the minimal level of quantification, which may be between 10 IU/ml and 20
IU/ml may seem reasonable [18].
Recommendations for serological testing with suspected pertussis
In neonates and young infants PCR and/or culture should be performed on nasopharyngeal samples,
nasopharyngeal swabs (NPSs) or nasopharyngeal aspirate (NPAs), as soon as possible post-onset of
symptoms. Measurement of IgG-anti-PT is only meaningful for older children/adults including parents
and other household members. In vaccinated children, adolescents and adults with less than two weeks
of coughing culture and PCR from nasopharyngeal samples should be done. For adolescents and
adults with coughing less than three weeks PCR and measurement of IgG-anti-PT should be
performed [1]. If coughing lasted at least 2-3 weeks, measurement of IgG-anti-PT should be sufficient.
In outbreak situations, PCR and culture should be done from nasopharyngeal samples and IgG-anti-PT
should be measured in serum samples.
Word count: 1998
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Deloria MA (1995) Description and evaluation of serologic assays used in a multicenter trial of
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Pediatrics 96 (3 Pt 2):570-575
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Robbins JB, Powell M, Mink CM, Poolman JT, Hildreth SW, Lynn F, Morris A (2009) International
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(2009) Characterization of reference materials for human antiserum to pertussis antigens by an
international collaborative study. Clin Vaccine Immunol 16 (3):303-311
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quantitative igg-anti-pt elisa for replacement of the cho cell assay. APMIS in press
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9. van Gageldonk PG, van Schaijk FG, van der Klis FR, Berbers GA (2008) Development and
validation of a multiplex immunoassay for the simultaneous determination of serum antibodies to
bordetella pertussis, diphtheria and tetanus. J Immunol Methods 335 (1-2):79-89
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in children and young adults. J Med Microbiol 55 (Pt 9):1223-1228.
13. Pebody RG, Gay NJ, Giammanco A, Baron S, Schellekens J, Tischer A, Olander RM, Andrews
NJ, Edmunds WJ, Lecoeur H, Levy-Bruhl D, Maple PA, de Melker H, Nardone A, Rota MC, Salmaso
S, Conyn-van Spaendonck MA, Swidsinski S, Miller E (2005) The seroepidemiology of bordetella
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14. De Melker HE, Versteegh FGA, Conyn-van Spaendonck MAE, Elvers LH, Berbers GAM, van der
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Bennett C (2005) A boarding school outbreak of pertussis in adolescents: Value of laboratory
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DP, Barenkamp S, Bernstein DI, Edelman R (2006) Bordetella pertussis infections in vaccinated and
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pertussis vaccine trial (apert). Clin Infect Dis 43 (2):151-157. Epub 2006 Jun 2005.
19. Marchant CD, Loughlin AM, Lett SM, Todd CW, Wetterlow LH, Bicchieri R, Higham S, Etkind
P, Silva E, Siber GR (1994) Pertussis in massachusetts, 1981-1991: Incidence, serologic diagnosis,
and vaccine effectiveness. J Infect Dis 169 (6):1297-1305
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incidence of pertussis in massachusetts adolescents and adults, 1989-1998. J Infect Dis 182 (5):14091416
21. De Melker HE, Schellekens JFP, Neppelenbroek SE, Mooi FR, Rümke HC, Conyn-van
Spaendonck MAE (2000) Reemergence of pertussis in the highly vaccinated population of the
netherlands: Observations on surveillance data. Emerg Infect Dis 6 (4):348-357
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single-sample serological technique for diagnosing pertussis in unvaccinated children. Eur J Clin
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11
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Table 1: Reference preparations from WHO and CBER/FDA
Values are given in IU/ml for the WHO preparations and in ELISA units (EU)/ml for the CBER/FDA preparations
IU/ml and EU/ml are numerically identical [##]
IgG-anti-PT
IgA-anti-PT
IgG-anti-FHA
335 IU/ml
65 IU/ml
130 IU/ml
65 IU/ml
65 IU/ml
42 IU/ml
106 IU/ml
18 IU/ml
122 IU/ml
86 IU/ml
39 IU/ml
38 IU/ml
CBER/FDA#3
200 EU/ml
15 EU/ml
200 EU/ml
100 EU/ml
ND
ND
CBER/FDA#5
ND*
140 EU/ml
ND
280 EU/ml
ND
90 EU/ml
CBER/FDA#4
ND
ND
ND
ND
90 EU/ml
25 EU/ml
WHO international
IgA-anti-FHA IgG-anti-PRN IgA-anti-PRN
standard (06/140)
WHO reference
reagent (06/142)
ND: not declared
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Table 2 Suggested cut-off values for IgG-anti-PT for adolescents and adults
Adapted from WHO Immunological basis for vaccination series (http://whqlibdoc.who.int/publications/2010/9789241599337_eng.pdf)
Country
Type of study
Cut-off
Sensitivity
Specificity
Reference
MA, USA
MA, USA
Population study
Population study
~ 100 IU/ml
~200 IU/ml
78%
67%
98%
99.9%
[19]
[20]
NL
Population study
125 IU/ml
62 IU/ml
70%
80%
99%
95%
[21]
D
Population study
50 IU/ml
80%
95%
[22]
EU
Epid. survey
125 IU/ml
n.a.
n.a.
[13]
USA
Epid. survey, model
94 IU/ml
46 IU/ml
n.a.
n.a.
n.a.
[16]
AUS
Clinical validation
50 IU/ml
better than 100 IU/ml
[17]
MA, Massachusetts.
n.a., not applicable.
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Appendix
List of participants of the EUpertstrain network
Members
Qiushui He and Jussi Mertsola
Carl Heinz Wirsing von König and
Marion Riffelmann
Nicole Guiso and Sophie Guillot
Hans Hallander and Abdolreza
Advani
Frits R Mooi and Guy Berbers
Anna Lutyńska
Karen Krogfelt and Tine Dalby
Norman Fry
Dorothy Xing
Camille Locht and David Hot
Clara Ausiello
Per Sandven and Jann Storsaeter
Email address
[email protected];
[email protected]
[email protected];
[email protected]
[email protected]
sophie.guillot @pasteur.fr
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]; [email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
[email protected]
Name of organization
National Institute for Health and Welfare
University of Turku
HELIOS Klinikum Krefeld
Town, Country
Turku, Finland
Institut Pasteur
Paris, France
Swedish Institute for Infectious Disease
Control
National Institute of Public Health and the
Environment
National Institute of Hygiene
Statens Serum Institut
Health Protection Agency
National Institute for Biological Standards
and Control
Institut Pasteur de Lille
Solna, Sweden
Istituto Superiore di Sanita
Norwegian Institute of Public Health
Rome, Italy
Oslo, Norway
Krefeld, Germany
Bilthoven, the Netherlands
Warsaw, Poland
Copenhagen, Denmark
London, UK
Potters Bar, UK
Lille, France
15